1. Field of the Invention
This invention relates to an image communication apparatus, a method of controlling the same, and a storage medium.
2. Description of the Related Art
In recent years, techniques in which a service is provided via a LAN or a next generation network (NGN), having replaced a conventional circuit switched public telephone network with a network based on IP (Internet Protocol) technologies, are widely used. Such NGNs (Next Generation Network) are provided with a bandwidth guaranteeing function and a security function in the network itself, and are IP networks that realize integrally services such as calling, video communication and data communication. Also, usage of an SIP (Session Initiation Protocol) in which a virtual session is established with a LAN or a communication device on an NGN, and a service is provided while the session is established has spread. On a communication device that has established a session by the SIP, a call or an image communication is performed by transferring PCM data with a plurality of PCM interfaces using a protocol such as IP or VoIP (Voice Over IP). With respect to image communication, there exists facsimile communication by ITU-T recommendation T.38 digital facsimile procedure, for example, and facsimile communication by ITU-T recommendation T.30 digital facsimile procedure (T.30 facsimile communication by a VoIP in-band communication).
In such a call or image communication, the transferring of the PCM data is performed by the plurality of PCM interfaces. In the transfer of the PCM data, a synchronous serial bus equipped with a data signal line and a synchronization signal line is used, and a data transfer side and another side are caused to operate as master and slave respectively. In addition, a case, in which transfer of PCM data is performed with a plurality of slaves by selectively switching and connecting the plurality of slaves to a master, is the same in that one side is caused to operate as the master while the other side is caused to operate as the slave, and bidirectional data transmission is performed at a data transfer timing of the master. In Japanese Patent Laid-Open No. 2005-202643, it is recited that a serial data communication is performed by a master in a case where a plurality of slaves are connected to a synchronous serial bus to which the master is connected.
Meanwhile, in this kind of apparatus that performs a call or image communication, in order to realize a power saving in a case where a usage frequency is low, it is common that automatically transitioning into a power saving mode be performed when an interval over which the apparatus does not operate is greater than or equal to a fixed interval. In such a power saving mode, a power supply and a supply of a clock signal to units other than a processing unit which is necessary to continue a function is stopped (for example, refer to Japanese Patent Laid-Open No. 2007-6518). The processing unit necessary to continue the function is, for example, one for an off-hook detection function in the case of a call. Accordingly, after transitioning into the power saving mode, in order to detect an off-hook of a receiver, a power supply and a supply of a clock signal to the processing unit for the off-hook detection is maintained.